Prevention of damage to welded joints of 12Kh18N10T steel in production of potassium nitrate

Abstract

'kyi, H. V. Chumalo, and V. I. Sumets ' UDC 620.194 We analyzed damage to welded joints of pipes made of 12Khl8N10T steel in working media for the production of potassium nitrate. We showed that the corrosion cracking of objects was caused by the action of chlorides in technological solutions under a high level of residual postwelded stresses in welded joints. We give some recommendations for the prevention of the corrosion cracking of welded joints of pipelines and pressure filters.In working media for the production of potassium nitrate at the industrial enterprise "Concern Azot", there appear corrosion cracks in welded joints of pipes with sizes from 025 x 2 to O 159 x 4.5 mm and bodies of pressure filters made of 12Khl8N10T steel welded with a TsL-11 (Sv 08KhI8N10T) electrode. Damage mainly occurs in the following aqueous solutions: KNO 3 (51%) + NaCI (49%) (t = 135~ and p = 0.5 MPa) and NaNO 3 (11.7%) + NaCI (11.2%) + KNO 3 (58.9%) + Na2CO 3 (-0.01%). In addition, under factory conditions, for the estimation of the sensitivity of steels to corrosive damages, one uses an aqueous solution-simulator: NaNO 3 (24%) + KC1 (21%) + NaCI (-1%) + Na2CO 3 (up to 0.01%) at 60-90~ Chlorides whose concentration can reach critical values in dead zones in the process of evaporating technological media from the surface of metal are likely to cause corrosion damages. Under these conditions, due to high residual welded stresses, the steel and the weld crack.The aim of this work is to establish reasons for fracturing of welded equipment and to develop recommendations for its protection.We investigated the sensitivity of plane specimens loaded by a constant strain to the corrosion cracking [1][2][3]. The specimens were made of a welded pipe with a size of ~ 89 x 4.5 mm that was not in service and of a nondamaged metal of the body of a pressure filter in the zone of welding. In the first case, they were cut out of a skelp along the pipe with a thickness of 4.5 mm; in the second case, the specimens were cut out perpendicularly to the welded joint. Moreover, the width of the specimen corresponded to the thickness of the cut-out equal to 16 mm (the thickness of the specimen was 6 mm).Stresses were given by a sap approximately at a level of 1 10, 220 (-~0.2 of 12Khl8N10T steel) and 330 MPa, i.e., respectively, 0.560. 2, 60.2, and 1.5~0. 2 of a given steel. For this scheme of loading ofspecimens, it was impossible to take into account the influence of strengthening caused by the weld which was not cut out and the effect of the curvature in the cross section of the specimen. The specimens were not treated across the thickness in order not to damage the inner surface and the welded joint, which contains postwelded defects (incomplete fusions, inclusions, and, sometimes, even crack-like defects). Some investigations were performed specially on specimens with defects to determine their potential danger for susceptibility to corrosion cracking. The axial welded seam (in one "batch") and the fusion line (in the second) coincide with the...